This disclosure relates to estimating the position of the center of mass of a downhole tool, the geometry of the borehole, and/or the mud parameter based on acoustic measurements, even when the downhole tool center is moving over time.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as an admission of any kind.
As a borehole is drilled, a logging-while-drilling (LWD) or measurement-while-drilling (MWD) operation may obtain a number of measurements using a downhole tool attached to the drill string. In a drilling environment, however, the position of the center of the downhole tool may vary substantially over one revolution. Indeed, the position of the tool center may vary by a few centimeters or more owing to the shocks and vibrations occurring in the vicinity of the drill bit. This variation of the tool center may result in measurement inaccuracies.
Furthermore, the geometry of the borehole is a substantial parameter of interest, since the geometry of the borehole provides useful information on the characteristics of the geological formation that surrounds the borehole. Because the relative displacement of the center of mass of the downhole tool may vary over time, however, a direct measurement of the borehole geometry while drilling may be difficult or may produce inaccurate results.
Some solutions for estimating the position of the tool center involve using an accelerometer to refer position of the tool center over time. While this may suffice over short periods of time, the accuracy of estimating tool center using an accelerometer quickly decreases over time. Moreover, when using an accelerometer, the position of the tool center may remain unknown with respect to the borehole geometry, which may vary at different depths. Additionally, while other techniques may involve performing multiple caliper measurements on the borehole, dividing the borehole into multiple different sectors, and identifying a histogram of measured radii, these techniques may be less accurate than desired and/or may require certain specific assumptions to complete.